Certain metal ions are known for having biocidal properties. Transition metal ions, such as silver ions and copper ions, as well as zinc ions, are used for their antibacterial properties. For example, silver ions have been used as a disinfectant or a germicide in the form of a solution of silver nitrate; however, silver nitrate is inconvenient and restrictive in use due to its solution properties. Polymeric materials incorporating such biocidal metal ions are used to avoid the handling problems encountered.
One method of incorporating the metal ions within a polymer is through the dispersion of zeolite particles. In this method the zeolite particles are employed as a carrier for the metal ion. These zeolite particles carrying the biocidal metal ions can be compounded into polymers such as polyethylene, nylon or polyolefin. Such methods are exemplified in Hagiwara et al., U.S. Pat. No. 4,911,899, herein incorporated in its entirety by reference. During the compounding process, these zeolite particles can be exposed to elevated temperatures. The range of temperatures used is dependent on the transition temperature of the polymer used. Such elevated temperatures make heat stable zeolite desirable.
Many methods presently exist for the production of zeolites to be used as biocidal metal ion carriers. Many, if not all, such processes include a step for drying the zeolite particle. One such drying step can be direct drying of the particles with combustion gases. However, such severe drying conditions create zeolite particles upon ion exchange with metal ions form particles which are more easily discolorable when exposed to ultraviolet light and/or elevated temperatures. To avoid such instability, the prior art has moderated such drying conditions, such as by the use of increased air volume in the drying gases. Such steps of moderation increase the length of the time of drying as well as the equipment costs. There continues to be a need for improved methods for the preparation of biocidal zeolite particles.